The need for compact and light portable medical modalities has been increased by changes in social situations, such as provision of home care systems and expansion in the range of emergency care. Recently, in order to respond to such a need, various medical modalities have been developed with the progress in analytical and diagnostic technologies in the medical field. Radiation imaging apparatuses having radiation generators are large in size and are therefore mainly installed in hospitals, medical examination institutions, and other facilities. The installed medical modalities have been utilized by regularly setting an operation period and an idle period including the time for maintenance.
Such a radiation imaging apparatus having a radiation generator is also required to be modified into a medical modality applicable to home care or emergency care for disasters and accidents by increasing the operating ratio of the apparatus through enhancement of durability and reduction of maintenance requirement.
One main factor that determines the durability of a radiation generator is the durability of the target serving as a source of generating radiation such as X-rays. The target generally has a laminated structure, and it is known that the maintenance of “adhesion” between the layers of the target for a long time is important for enhancing the durability of the target.
In a radiation generator that generates radiation by irradiation of a target with electron beams, the “radiation generation efficiency” of the target is less than 1%, and the majority of the energy injected into the target is converted into heat. If the “dissipation” of heat generated in a target to the outside of the target is insufficient, denaturation of the materials constituting the target and problems in “adhesion”, such as peeling of a film due to the stress occurring in a layered structure, may occur.
It is known that “radiation generation efficiency” can be increased by using a transmission type target constituted of a thin-film form target layer that contains a heavy metal and a base material that transmits radiation and supports the target layer. PCT Japanese Translation Patent Publication No. 2009-545840 discloses a transmission type target of a rotating anode type having a “radiation generation efficiency” increased to 1.5 times that of a known reflection type target of a rotating anode type.
It is known that the use of diamond as the base material supporting the target layer of a transmission type target can accelerate “heat dissipation” from the target to the outside of the target. PCT Japanese Translation Patent Publication No. 2003-505845 discloses that the use of diamond as the base material supporting a tungsten target layer enhances heat dissipation and realizes microfocus. Diamond has high heat resistance and high thermal conductivity and also has high radiation transmissivity. Accordingly, diamond is a suitable material as a supporting base material of the transmission type target. The transmission type target of the present invention also employs a configuration in which diamond is used as a base material supporting the target layer.